ppm (parts per million) is the measure of concentration of greenhouse gases in the atmosphere. CO2 eq (Carbon dioxide equivalent) is a standard unit for measuring carbon footprints. The idea is to express the impact of each different greenhouse gas in terms of the amount of CO2 that would create the same amount of warming. Apart from CO2 they include methane (CH4), Nitrous oxide (N2O), Ozone (O3), and chlorofluorocarbons (CFCs).
